Wikipedia:Reference desk/Archives/Science/2010 August 3

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August 3

How to attach ceramic capacitor to solderless breadboard?

Ceramic capacitors are very small and have no wire legs, so how are they usually connected to a solderless breadboard? I could solder some wires on to form legs, but is that the usual solution? ----Seans Potato Business 01:05, 3 August 2010 (UTC)

No wire legs? I take it that you're using surface-mount components, then...? In principle, there's no technical reason not to solder legs on to them for breadboarding (the usual cautions about being careful not to overheat the component while soldering apply). But honestly, you can probably save yourself a fair bit of time and frustration (and possibly some slightly singed fingers) by investing in a few handfuls of assorted small ceramic capacitors with leads. They're pennies apiece if you can find a suitable store; they'll look like the brown one in the upper right corner of the top photo accompanying the capacitor article. (Hint — you're looking for a shop that has a wall of unpackaged electronic bits in little trays and drawers; a good place to look is near a university with an active electrical engineering program.) TenOfAllTrades(talk) 01:57, 3 August 2010 (UTC)

Right - the fact that it's potted in ceramic has nothing to do with the fact that it's packaged as a surface mount device. Potting and packaging are related but different parts of the mechanical design of electronic components. You can buy ceramic capacitors in all sorts of different packages. (I guess in the specific case of capacitors, "potting" is probably not even exactly right. Unlike other ceramic potting (e.g., for an IC), the dielectric layers in a cap are super-thin - they're probably CVD'ed, sputtered, or grown as an epitaxial layer). Nimur (talk) 03:25, 3 August 2010 (UTC)

Grr, I hate that problem. For the really tiny SMT ones, it's very difficult just to hand solder on leads, as the component, and the terminals, are so tiny. When I've done that in the past I've needed a little fragment of board (I think I had hardboard to hand) to hold things in place. I poked holes in it for the leads to give some stress relief (the solder bonds being so tiny they're not trustworthy to mechanically hold the leads on), threaded the leads through those, and soldered two little pools of solder at the far end, onto which I dropped and quickly resoldered the SMT component. The trick is preventing a bridge forming between the two pools; I think I needed more flux (proportionately) than usual, as the little spheres solder wants to form into are boulders compared with a little 3mm SMT part. -- Finlay McWalter • Talk 11:01, 3 August 2010 (UTC)

One of my colleagues suggests the following hack: take two insulated wires and tape them together, forming a slightly rigid wire object. Hotglue the SMT component lengthways on this. At one end of the component, burn the insulator off one of the two wires (with an old soldering-iron tip), put a sliver of solder in the gap (between the exposed wire and the terminal of the SMT component) and squish the wire-solder-component sandwich together with the heated iron, forming a bond. Do likewise with the other lead at the other end. -- Finlay McWalter • Talk 12:09, 3 August 2010 (UTC)

A picture of this is here. -- Finlay McWalter • Talk 12:12, 3 August 2010 (UTC)

Adapters exist for using SMT components on breadboards. Digi-Key (etc.) carry these, search for 'Surf-boards'. 128.95.172.173 (talk) 00:59, 7 August 2010 (UTC)

What benign medical conditions are easily misdiagnosed as a deadly incurable condition?

For a short story I’m working on I’m looking for a chronic benign condition which is often misdiagnosed as a lethal, incurable condition. To fit the needs of the story, the lethal condition should also be typically relatively non-debilitating for a few months to a year. This should be the kind of mistake which could actually be made, even with analysis by a specialist and a variety of tests. Thank you for helping me make my writing as scientifically accurate as possible. --S.dedalus (talk) 02:42, 3 August 2010 (UTC)

[1] suggests Aortic dissection - which can be mistaken for heartburn. Dunno that it would still be mistaken after specialists and tests had been done though.

[2] suggests that strokes in people under the age of 45 are misdiagnosed as a bunch of relatively mild diseases.

SteveBaker (talk) 02:55, 3 August 2010 (UTC)

Thanks Steve, but I'm actually looking for benign conditions which could be misdiagnosed as deadly ones. A traumatic but fortunate turn of events to be sure! --S.dedalus (talk) 03:03, 3 August 2010 (UTC)

Doesn't it follow that if A can be misdiagnosed as B - then B can be misdiagnosed as A? The situation doesn't often happen the way you describe because if something benign (like indigestion) gets misdiagnosed as something serious (a heart attack) then immediately, everyone rushes around, gets in experts, does detailed testing - and eventually discover that it's really something benign. It's only in the reverse case where the misdiagnosis tends to go undiscovered until the condition gets much worse. SteveBaker (talk) 14:03, 3 August 2010 (UTC)

Perhaps it's different in places with good state funded medical care. If you attend Casualty at an Australian hospital with indigestion and the symptoms of anxiety from the fear that you may be having a heart attack, you'll be treated as if you're having a heart attack - several hours of monitoring followed by an appointment with a cardiologist. --203.202.43.53 (talk) 06:35, 4 August 2010 (UTC)

Haha. I find it funny you slip some politics into your non-response. Shadowjams (talk) 06:36, 4 August 2010 (UTC)

I'm not sure there is anything that meets all your conditions. If there is something that is "often" misdiagnosed, specialists quickly become aware of it and get more careful with their diagnoses. The closest thing I'm aware of is that benign forms of prostate cancer are pretty frequently misdiagnosed as aggressive forms -- but at the stage where this can happen, even the aggressive forms are still treatable. Looie496 (talk) 04:17, 3 August 2010 (UTC)

True. I didn't mean to imply this had to be a common occurrence. It could be something extremely unusual. A rare genetic condition or something perhaps. --S.dedalus (talk) 06:17, 3 August 2010 (UTC)

Your best chance is to just go with a technical error. True story - when I was 22 I blew out my right knee's ACL in a basketball game, but didn't realize it (thought it was just a sprain). The swelling went away pretty quick and I got on with my life. 3 months later I went to see an orthopedic specialist because that knee had some persistent swelling in the rear. He ordered an MRI, after which he informed me I had cancer in the lymph node(s?) in my knee. A second opinion revealed the blown ACL (and the first doctor to be an idiot), but for a full 72 hours my entire family thought their otherwise healthy 22 year old son was dying of KNEE CANCER. Bizarre. 218.25.32.210 (talk) 04:56, 3 August 2010 (UTC)

Wow, sorry to hear that! It must have been quite a scare. I had a roommate a while back that was told by a doctor that his wracking coughs and chest pain was "allergies." A more competent doctor realized that he was actually suffering from a spot of pneumonia. :) --S.dedalus (talk) 06:30, 3 August 2010 (UTC)

I can't really think of anything benign that can be misdiagnosed as a lethal condition except, perhaps, rarer forms of benign skin carcinomas/melanomas? A tumor can be benign (i.e. not invasive to surrounding tissues) or cancerous (where it starts to invade other tissues, and perhaps metastasize around the body). I imagine there are certain benign tumors, probably the rarer ones, that can initially appear as potentially cancerous but which later, after biopsy, are revealed to be benign. Problem (or not!) with this is that no doctor would say "you've got cancer", they'd say something along the lines of "this looks suspicious, so we'll check it out with a biopsy". So they're not going to misdiagnose you on the spot with cancer of the skin.

Thanks for the help everyone! How about multiple sclerosis? From what I've been reading, it sounds like MS diagnoses are extremely difficult to make and rather subjective. Is it possible for some, perhaps rare, condition to have all the symptoms of MS but slip through the battery of tests they put suspected patients through? --S.dedalus (talk) 06:30, 3 August 2010 (UTC)

I don't think MS fits the bill for a benign medical condition. People with MS do live long lives with proper care, but the life expectancy is still shorter than people without MS. Keeping that aside, I can't think of any diseases that have the same symptoms of MS without causing harm, because the very nature of MS is demyelination which is bound to have bad side effects. Regards, --—Cyclonenim | Chat  11:19, 3 August 2010 (UTC)

Here's a short-term one: marathon runners and other endurance athletes sometimes develop left ventricular hypertrophy, where the left ventricle of their heart grows abnormally powerful (to assist them in their exercise); this changes their cardiac rhythm, but is perfectly healthy. But LVH is also caused by heart disease, and also manifests itself as an unusual cardiac rhythm. So it's not unheard of for a scenario like this to happen: during a race, an marathon runner develops a minor injury (such as a scraped knee following a trip) which takes them to the on-course medics. These folks give them the once-over (which is wise, as that trip could have happened when the person felt faint, even though they don't remember it now) and listen to their hearts. People who work, or volunteer, as on-course medics are often nurses or EMTs during the day, so they're not used to dealing with serious athletes but very often see heart attacks and arhythmias in the general public. They listen to the athlete's heart, hear that weird left ventricular sound, and think it's heart failure. And as the runner has other symptoms that they've come to associate with heart problems (tachycardia, fatigue, breathlessness, sweating) they're prone to treat the person as if they're in the midst of a serious coronary episode. And it's hard to tell these people to ignore their training and experience, as genuine heart patients often deny they're seriously ill, and people really do die from genuine heart attacks during marathon races. The medics want to ship the runner off to hospital for proper investigations (which will quickly determine he's a freakish, but healthy, specimen), but the runner doesn't want his race ruined. I've heard of at least one case where runner, still with bleeding minor injury, escapes the tent and leads a band of medics off in pursuit, yelling to them that if he's really got heart failure then they should be able to catch him. Which is all very funny, unless he really has had a heart attack. -- Finlay McWalter • Talk 11:32, 3 August 2010 (UTC)

To meet your full criteria (that of misdiagnosis for a lengthy time) would require some pretty bad, and very under-resourced, doctors. -- Finlay McWalter • Talk 11:39, 3 August 2010 (UTC)

An easier approach — depending on the plot — is to make the patient do their own research on it. "Oh, hmm, chest pains — oh my! I'm dying!" ... and then it turns out to just be gas. Not a great example but you can see the gist. It would also ring familiar — how many of us have Googled funny little symptoms ("why do I have a pain here?") and then find that one of the possible reasons (with no indications given of probability) is, you know, that we have Ebola or something. Obviously that would require some retooling of the plot, but somebody slipping into a bit of hypochondria can be a wonderful character development... --Mr.98 (talk) 12:24, 3 August 2010 (UTC)

How about a complicated set of benign conditions which when taken together provide all of the symptoms of something serious? That ought to be relatively easy to figure out. Just pick out a suitably serious medical condition, then look at all of the symptoms it produces and hypothesize that your character has half a dozen minor ailments that happen to add up to meeting all of the symptoms. It might make a neat plot point to have some of the individual symptoms disappear one at a time. SteveBaker (talk) 14:03, 3 August 2010 (UTC)

That's sometimes known as medical student syndrome. The problem is that the question also requires specialists to be fooled after performing tests. Without that requirement it's easy. Looie496 (talk) 17:42, 3 August 2010 (UTC)

This is a great question though. I'm sorry, I don't have the background to really answer this well, but I bet if I rewatched enough House I could come up with one... if you don't get a good answer here I'd actually suggest reasking it again soon because I'm sure there're some interesting answers to this from med students / very bored doctors. Shadowjams (talk) 04:39, 4 August 2010 (UTC)

Pheochromocytoma (PCC) is a rare, but potentially lethal (if unnoticed and it leads to malignant hypertension or hypertension) condition and can be misdiagnosed as straightforward hypertension. In my case, my doctor explored the possibility of PCC due to my relatively young age and high blood pressure. I can imagine a situation where a doctor wouldn't consider it for an older patient, for the purposes of fiction, of course! --Rixxin (talk) 15:56, 4 August 2010 (UTC)

Interesting problem with AM Radios...

I wasn't quite sure whether or not to post this in the Computing Reference Desk, since it seems too low-tech for that page. Anyway, here goes.

I live in a 3,000 square foot 2-story house that's on a lot that's about 90 feet wide by 120 feet long. (From me looking out my window, but my sense of perspective is sometimes very off). The hill that our house is on is about 325 feet about sea level, and it slopes down gently to river level (I don't believe it's sea level) over the course of just over a mile. The town overall gets fairly decent AM reception on most local channels. However, since a week or two ago, the AM reception in our house's lot has completely disappeared. Whenever we are driving home from anywhere and we have the AM radio on, the radio works fine as we are driving down the road, but all of the channels go from clear to static (over the course of 10 feet or so) right as we pull into our driveway. This is the same for any other AM radio that is on our lot. FM works just fine, and so does any other sort of wireless communication except AM. The local AM channels also work on the properties of the 30+ other houses on our street. It's almost like there is an "AM black hole" that encompasses our property. I thought that it might have been our wireless router (which we had repositioned the antennas around the same time this ordeal started) causing the trouble, but the other members of my household (one with a ham radio license) believe this is not the case. It is nothing severe (it's not like we are in a place where the only way we get news is from AM stations), but it just seems a little strange. Could there be anything (electronic or geological) that is causing interference with the AM band? Any insight (be it professional or not) would be greatly appreciated. Hmmwhatsthisdo (talk) 04:18, 3 August 2010 (UTC)

This is a case of radio frequency interference. You can try to determine what it is by powering down everything in your house, and possibly neighbour's houses too. Nowadays switchmode powersupplies, computers, motors, video equipment, compact fluorescent lighting, can all put out interference in the megahertz range. You may have to change your light globes to tungsten to reduce the interference. Graeme Bartlett (talk) 06:12, 3 August 2010 (UTC)

... or ask of yourselves and possibly your immediate neighbours "What was switched on for the first time a week or two ago?" You should be able to tell the difference between RF interference and just weak signal (the static usually sounds harsher for RF). I notice that certain houses suffer this problem as I drive past whilst listening to my car radio. Christmas lights are a common cause, but freezers, motors and lots of other appliances can cause the problem, especially if the are run at some distance from the electricity supply. Fluorescent lights should cause only a very local interference unless they are faulty. Dbfirs 08:11, 3 August 2010 (UTC)

Yes, but neither my house nor my neighbor's houses (as far as I know) have installed anything new when the problem started. Also, their houses do not have any sort of interference to speak of. However, I just noticed today while driving home that the area of interference has decreased ever so slightly, by about 2 feet or so. It is definitely NOT weak signal, as all of the channels (not just one) drop out to static over the course of 5 feet or so. However, the list of possible causes for interference is helpful, and I will check with my neighbors later and see if they did happen to install anything. It just seems odd that such interference would happen so suddenly, and it seems unlikely that something in a neighbor's house could cause interference in our house. Hmmwhatsthisdo (talk) 00:37, 4 August 2010 (UTC)

It's possible that the cause is some appliance that has just started to malfunction. Have you tried carrying round a portable radio to determine where the interference is strongest? Dbfirs 06:32, 4 August 2010 (UTC)

It indeed sounds like there is a new source of radio frequency interference near your house. The source is often power company equipment. I have seen two utility ground wires touching and the small voltage between them was enough to interfere with radio reception. The FCC in the US is in charge of getting the creator of such "harmful interference" to shut it down, but they are grossly understaffed. The local power company might have personnel who could track it down if you call in and complain, but only if you insist the interference is coming from their equipment. I have known them to track it down to a light fixture in the neighbor's attic, or the new pizza oven in the corner restaurant. It is extremely hard to do "direction finding" and locate the interference. It is more process of elimination. It could be a malfunctioning doorbell, any electric appliance, a furnace ignitor, a fluorescent light, dimmer switch, low power radio transmitter such as a garage door control, or an aquarium heater. You might listen on your car radio, then kill the power in the house (taking precautions that no one is startled and nothing essential gets shut off) and see if reception improves. Then try to get the neighbors to do the same if it is not on your premises. Edison (talk) 03:27, 5 August 2010 (UTC)

Brand name drugs vs generics

I read the wikipedia article about generic drugs, but I am having a hard time understanding why a generic drug can really differ from the brand name. I have customers who use all generic drugs and don't have any problems or complaints with any of them. But those same people, when switching from brand to generic on certain drugs have a problem. An example would be generic Wellburtrin XL, both the 150mg and 300mg. Its a widespread problem. Almost everyone complains about it, not just one or two people. So I know there is a real issue. There are a few other drugs out there that really seem different than the brand name. I'm convinced it's not just in the head of my customers because they use other generics with no problems. Since the FDA regulates all generics and tests them also and I'm sure by now they have heard about it and would have done something if there was a chemical difference, what could be an explanation to the problem? —Preceding unsigned comment added by 76.169.33.234 (talk) 04:59, 3 August 2010 (UTC)

Tell the FDA , not us. Sf5xeplus (talk) 05:23, 3 August 2010 (UTC)

It is quite possible that the generic is manufactured at a different plant or by a different company than the brand name drug. Differences in manufacture could have differing standards of quality control, which may lead to problems. --Jayron32 05:44, 3 August 2010 (UTC)

From the "generic drugs" wikipedia article, the difference between two batches of the same brand name drug is about 3.5%, which is about the same between a batch of a brand name drug and a batch the its generic. So I don't think that's it either. Also, many of these generic manufacturers are very reputable and their products are tested and they get audited. So even though it could be a very short term problem, it wouldn't be a long term problem as this one is.

It could perhaps be an example of the Placebo (or Nocebo) effect, based on the patient's belief that a generic drug is somehow not the real thing. AndrewWTaylor (talk) 09:42, 3 August 2010 (UTC)

I mentioned that they have no problems with the other generics they are taking for this reason...

I once had a problem with a generic that used different inactive ingredients than the brand name drug, and it turned out I had an allergic reaction to one of them. Since the inactive ingredients are generally chosen to be pretty common and benign substances, I would assume it is pretty rare to see such a reaction, but I don't know how rare. Dragons flight (talk) 10:41, 3 August 2010 (UTC)

This is just a guess, but two things come to mind. The first is the inactive ingredients, as Dragons flight mentioned. The packaging of generic medications often says something like "the same active ingredient as (some brand name drug)", implying that the inactive ingredients are not the same. A second factor is quality control. I've read an anecdote from someone who supposedly was in the pharmaceutical industry. The person said that the internal quality control standards were tighter for the brand name drugs they made than the generic ones they made. In that story, the person was talking about variation in the amount of active ingredients in the manufactured drugs. I guess lower quality control standards may also affect the types and levels of impurities in the products. --173.49.16.4 (talk) 11:42, 3 August 2010 (UTC)

While the active ingredient is the same between a brand name and a generic drug, the pill itself is not the same. A pill is not just the drug. It is also a coating that dissolves in the body to release the drug at the right time. For many drugs, the release is performed in small increments over time. The FDA does not strictly regulate when and how a drug is released in the body.

Of course it does. It must be equivalent and have the same bio-availability.

So, consider something like a blood pressure medication that is marked at "extended release" (I am purposely avoiding a specific brandname because of my job). A brand name drug is more expensive. The expense is not just because it is a brand name drug. The expense is also for quality. That expensive pill may have 100mg of a drug that releases 10 times over 24 hours in 10mg doses. Then, consider the cheap generic. It also has 100mg of the same drug and it is extended release, but it releases 50mg right away and 50 mg 12 hours later. In a 24 hour period, they release the same amount of medication, but the brand name drug is clearly better at control. The goal is to increase release of the drug into smaller and smaller quantities over a long period of time.

If your argument were true, people would die from a generic form of a blood pressure medication.

So, why is the generic so bad? Why don't they make it release multiple times instead of two big doses? The same drug companies that make the brandname drugs also make the generics. They want people to buy the brandname drugs. So, they purposely make the generic ones much cheaper and lower quality. For many people, the generic is acceptable. For others, the generic is not. Thus, a market for the brandname drug is maintained after the generic hits the market. -- kainaw™ 12:08, 3 August 2010 (UTC)

"The same drug companies that make the brandname drugs also make the generics." While this is sometimes true, often it is not: most generics (by volume) are made by other companies than the originator of the licenced brand-name drug, when the latter's patent has expired. Generic manufacturers can do so more cheaply because they're not amortising any of the very considerable research, trialling and licencing expenses the brand-name originator had both for that drug ("molecule" in the trade) and around nine others that never made it all the way to market, which averages out to (I believe) around a billion US$ per marketed drug.

Apart from the considerations that Kainaw and others have mentioned, a possible further factor is counterfeiting. Making fake drugs and inserting them into the legitimate pharmaceutical trade (as well as selling directly online) is very big international business. While licenced brand name drugs are dearer and therefore more lucrative to fake, they are protected by anti-counterfeiting measures, which include (but are not limited to) markings on the tablets/capsules and coded information on the packaging, as well as procedural checks. The standard of such protections for generic drugs are likely somewhat lower and thus easier to overcome, and the markets for generics in some instances less alert, so generics too will be widely - perhaps more widely - faked and thus may have inappropriate levels (from too much to none) of the supposed active ingredients and possibly other ingredients actively harmful or more widely allergy-provoking. [Disclosure: I used to work in (non-pharmaceutical) administration at a large pharmaceutical manufacturing site.] 87.81.230.195 (talk) 13:58, 3 August 2010 (UTC)

"So, they purposely make the generic ones much cheaper and lower quality" — citation needed. Do you even have any evidence that it is the same companies making both generics and brand name? This strikes me as highly unlikely on the whole. If you are going to make these kinds of assertions and generalizations (which smell of old wives' tales), please cite them, lest we fall into rumor-repeating. --Mr.98 (talk) 13:55, 3 August 2010 (UTC)

From Merck here, "In fact, generic drug makers manufacture many trade-name products for companies that control the trade names. Sometimes, more than one generic version of a drug is available." Merck is a drug company that produces both brandnames (trade names) and generics. -- kainaw™ 17:09, 3 August 2010 (UTC)

A bit of OR from Australia here.... I regularly use medication for hay fever, and am happy to use generics, usually having no problem with them at all. Once I tried a new generic, and found very reduced performance. A close read of the packaging showed "Made in India". Most of our medications are made locally. I spoke later to my pharmacist, who said I wasn't alone in my experience, and he was no longer stocking that product. Make of this story what you will. HiLo48 (talk) 12:38, 4 August 2010 (UTC)

Cold object

Suppose an object is cold but doesn't change temperature easily. Will it feel cold to the touch? 81.137.101.82 (talk) 13:25, 3 August 2010 (UTC)

If it is colder than your hand, it will feel cold. "Cold to the touch" means that it is colder than your hand. It is a very poor measure of temperature. -- kainaw™ 13:32, 3 August 2010 (UTC)

"Doesn't change temperature easily" is a somewhat confusing phrase. Let's consider instead materials that conduct heat easily (like metals) versus those that are good insulators (like maybe wood). If you chill down a block of steel and a block of wood to the same temperature and put your hands on each of them - then the steel feels much colder to the touch than the wood does even though they are at the same temperature. That's because your skin isn't measuring the temperature of the material you're touching so much as the rate at which the skin is giving up heat to that material. The steel, conducts heat away from your hand easily - so (assuming it's colder than you are), it feels very cold to the touch. It'll continue to conduct heat away until the whole chunk gets warmed up to your body heat. The wood, on the other hand, conducts away just enough heat to warm up the surface of the wood to body heat - but because it's a good insulator, that thin warm layer insulates you from the colder stuff inside. The heat from your hand doesn't easily spread out into the bulk of the material. So right where you're touching it, the wood rapidly reaches body heat and the sensation of it being cold to the touch disappears. The bulk of the wood is still quite cold though - and it would take an enormous amount of time for your body heat to warm the entire block up.

The opposite happens when you touch something hotter than skin temperature. A block of hot metal will transmit heat into your hand quite easily - where a block of wood won't - so the metal feels hotter than the wood.

SteveBaker (talk) 13:52, 3 August 2010 (UTC)

Note that 'doesn't change temperature easily' could also mean the object has a high specific heat capacity. This is also likely to make a difference to how cold an object feels particularly over the long term. But I'll let someone else expand on that (my quick search didn't find anything but a lot of confused discussions) Nil Einne (talk) 16:52, 3 August 2010 (UTC)

Indeed, the heat capacity is the best interpretation of the difficulty in changing temperature. It is the amount of energy required to increase the temperature by a certain amount. If an object has high heat capacity (total heat capacity for a conductor, specific heat capacity for an insulator) then it will take longer to change temperature to match your hand, so it will feel colder/hotter for longer. For something like wood (an insulator with pretty low specific heat capacity), the bit you touch warms up to the temperature of your hand almost instantly, which is why it doesn't feel cold. If it had a much higher specific heat capacity, then it would take longer to warm up and you would initially feel it as cold. --Tango (talk)

Heat capacity is not enough. Much more important is heat transmission, i.e. insulation. Ariel. (talk) 17:17, 3 August 2010 (UTC)

That's more important in determining whether something feels cold, but it's not more important in answering the OP's question, since the question was clearly about ease of changing temperature, not ease of transferring heat within itself. --Tango (talk) 19:03, 3 August 2010 (UTC)

Still, the question was not this complicated. It was merely "Will it feel cold to the touch?" Discussing how cold is another topic all together. -- kainaw™ 19:07, 3 August 2010 (UTC)

The answer to your question is "No.", it will not feel (as) cold. Skin does not measure absolute temperature - but it doesn't measure relative temerature either. It measure change in temperature, specifically how fast heat is drawn off, or added to, the skin. This is why 75 degree air feels warm, while 75 degree water will feel cold. Note that the hypothalamus does measure absolute temperature, and works differently from the skin. Ariel. (talk) 17:14, 3 August 2010 (UTC)

Well, let's look at an example. What doesn't change temperature easily? Something like glass or ceramic, right? Does a cold glass or ceramic object feel cold to the touch? I don't think I need to answer that. Looie496 (talk) 18:22, 3 August 2010 (UTC)

They don't feel cold because they are thermal insulators, not because they have high specific heat capacity. --Tango (talk) 19:03, 3 August 2010 (UTC)

75F metal feels cooler than 75F plastic for the reason that the metal cools your hand faster. John Riemann Soong (talk) 19:16, 3 August 2010 (UTC)

Glass and ceramic still conduct heat away from skin better than wood and plastic does. --Chemicalinterest (talk) 19:50, 3 August 2010 (UTC)

sulfonates and cells

Do sulfonates have any signalling roles in cells? Ignoring pH considerations, can the presence of them inside a cell cause apoptosis? Are sulfonate ligands less likely to repel each other than carboxylate ligands? John Riemann Soong (talk) 16:26, 3 August 2010 (UTC)

What sulfonate and cells are you experimenting with? One source suggests that sodium tanshinone IIA sulfonate (STS) protects against stress-mediated apoptosis in cardiomyocytes. Regards, --—Cyclonenim | Chat  16:31, 3 August 2010 (UTC)

Wow thanks for the rapid response. =) Umm, I don't actually have the sulfonate -- rather I'm concerned about it being produced when I react hydrogen peroxide and gold nanorods with sulfur-attached carboxylate ligands of various alkyl lengths (I think 7 carbons maybe? I don't know if there are PEG motifs -- the company I bought these rods seems to keep it a secret). I am trying see if there's a side reaction between hydrogen peroxide (at 200 micromolar) and these thiol-attached linkers. It is my hope that the gold-sulfur bond inhibits oxidation, but if not, I suspect the bond may break and that the linker might be turned into a sulfonic acid, e.g. a sulfonate (since the rods are diluted and the linkers are found only on the surfaces I really doubt it will change the pH that much).

I'm working with a549 cells. I know many of the rods survive intact without aggregation (aggregation would be one symptom of the nanorods losing their sulfide-bound linkers) and cells endocytose them successfully. However I wonder if a minute amount of the linkers could be oxidising into sulfonates and poisoning the cells. One paper reports that a549 cells can actively grow at concentrations of 200 micromolar hydrogen peroxide, but that was without the presence of things like gold nanoparticles. John Riemann Soong (talk) 16:48, 3 August 2010 (UTC)

Sorry about the not so rapid response this time! I think that unless you have a reason to believe the gold nanoparticles are going to affect the growth of the cells from previous experiments, there's no reason to believe it'd have any effect on the growth with minute quantities of H2O2. I'm guessing either your stock of cells or gold nanoparticles are limited; if not, just give it a go? It's half the fun of experimentation. If it fucks up, it fucks up. That's science! Regards, --—Cyclonenim | Chat  18:41, 3 August 2010 (UTC)

Whoops, just realised I overlooked a sincere part of your first paragraph. This is above my head really, you're a year ahead of me and a biochemist as opposed to a biomedical scientist. I think the above is as far as I can speculate really! Regards, --—Cyclonenim | Chat  18:44, 3 August 2010 (UTC)

stochiometric tests for hydrogen peroxide

What are some quick and dirty tests I can do to test for hydrogen peroxide and if possible, measure how much left is in solution? I do not think I have any thiocyanate and phenolphtalein in my lab, but I could check... John Riemann Soong (talk) 16:38, 3 August 2010 (UTC)

I have some ascorbic acid and pH paper...I sense some nasty acid dissociation calculations coming up, but does ascorbic acid react with hydrogen peroxide instantaneously? John Riemann Soong (talk) 17:10, 3 August 2010 (UTC)

Any of these any use [3] 94.72.239.127 (talk) 19:17, 3 August 2010 (UTC)

Regarding mixture of hydrogen peroxide and ascorbic acid: I think it needs a catalyst. I occasionally mix tainted H2O2 and ascorbic acid and get a hot test tube almost instantaneously. But when I try to do it deliberately, it never works. --Chemicalinterest (talk) 19:45, 3 August 2010 (UTC)

You've never intentionally tried it in the presence of your iron(III) chloride? Not that I want to use a Lewis acid catalyst, seeing as how that might make the calculations harder. My orgo prof used to tell me that some quick and dirty recipes for Friedel-Crafts reactions used to be: add in your organic reagents...add HCl...drop in a rusty iron nail...cover reaction vessel, wait 10 minutes (or 2 hours, depending on reaction). John Riemann Soong (talk) 15:01, 4 August 2010 (UTC)

Not eating with tablets

The instructions on my medication say that I have to take them on an empty stomach, or one hour before eating. Why is this, what relevance will my pepperoni pizza have to my tablet? (I'm assuming here that it's a general rule and not a specific necessity of this drug, but just in case, it's flucloxacillin.) Vimescarrot (talk) 17:34, 3 August 2010 (UTC)

Some research has led me to note that it is not a tablet, but in fact, a capsule. Who knew. Vimescarrot (talk) 17:37, 3 August 2010 (UTC)

No it's specific to this drug. Specifically: "Floxapen is extremely well absorbed orally. A single 250 mg dose achieves an average peak serum level virtually equal to that achieved by an equivalent IM injection. The peak serum level is achieved half to one hour after administration. Floxapen should be taken 1 hour before meals to ensure that maximum absorption is achieved." Basically what they are saying is that by taking it with food you slow down the absorption, but for this drug it's better if it has a very high peak absorption (presumably to kill as many bacteria as possible with a sudden strong dose). Other drugs are different, for them you might want slow and steady. Sometimes they say to take with food because it causes stomach upset. Ariel. (talk) 18:05, 3 August 2010 (UTC)

Oh. Well, that clears that up. Thanks. Incidentally, does anyone know how I might stop burping up that awful taste afterwards? Vimescarrot (talk) 21:13, 3 August 2010 (UTC)

Tic Tac? DaHorsesMouth (talk) 22:58, 3 August 2010 (UTC)

In addition or perhaps more accurately a more extreme form of avoiding stomach upset, with some NSAIDs, taking with meals helps reduce the chance of getting a peptic ulcer and other similar problems like bleeding. [4] Nil Einne (talk) 06:07, 4 August 2010 (UTC)

what happens when PBS cell buffer is exposed to air?

I left the cap open for 1 whole day ... it wouldn't be infected or be oxidised by now...would it? John Riemann Soong (talk) 18:43, 3 August 2010 (UTC)

If you are talking about phophate buffered saline, then I think that there is nothing to worry about. It should be pretty unreactive, so it won't oxidize, and it is unlikely to grow any bacteria (if it could, it would proably do so even with the lid on). Unless something actually fell into the open bottle I think that it should be fine.24.150.18.30 (talk) 02:12, 6 August 2010 (UTC)

Traveling to nearby stars

After looking at this site, http://kisd.de/~krystian/starmap/, I was asking myself the following question:

When we decide to travel to any of this nearby stars, with current technology, it is an advantage if the star is not too far to the 'north' or 'south' of us?

I mean, so far, while traveling in our own solar system, we've never been 'up' or 'down' very much. Is this really more difficult without the slingshot acceleration you get from traveling past planets? Or is just that there is nothing special to see/do?

Of course, I understand that Proxima Centauri is the least far away, so it's quite logically the easiest star to travel to, just wondering if moving up or down is harder to do.

Thanks. Sealedinskin (talk) 19:43, 3 August 2010 (UTC)

The solar system is so miniscule compared to the distance between it and the nearest star that it will make very little difference. A down-to-earth equivalent would be a centimeter (inch)-high hill. --Chemicalinterest (talk) 19:47, 3 August 2010 (UTC)

(Pedentry attack! Can . . . not . . . resist!) The word is traditionally, and correctly everywhere but the USA, Minuscule :-) . 87.81.230.195 (talk) 20:53, 3 August 2010 (UTC)

"Pedantry". --Sean 21:09, 3 August 2010 (UTC)

One of my very common mispellings (oops, there's another one). --Chemicalinterest (talk) 22:07, 3 August 2010 (UTC)

It's not a question of distance, it's a question of whether a gravity assist would be useful for travel to a neighboring star. Intuitively I think it's unlikely you could get a big enough one to matter much, but I don't actually know. Looie496 (talk) 20:00, 3 August 2010 (UTC)

Relative to its size the milky way is flatter than a sheet of paper[5] (i.e. ratio of thickness to diameter). So it's not necessary to travel very far north/south (up/down? above/below?). Ariel. (talk) 20:36, 3 August 2010 (UTC)

Well, we're talking about nearby star systems. It's not flat on that scale. Looie496 (talk) 20:50, 3 August 2010 (UTC)

(ec) The most straightforward kinds of gravity assist, if used within our own solar system, would suggest a star on the plane of the ecliptic is easier to reach. If the plan is to travel quite distantly beyond that, using gravity assists, I would surmise that any gain in the local sense within our own solar system would be insignificant. Note that our ecliptic is not coplanar with the galactic equator, so a boost in the plane of our solar system would send us out of the galactic plane. Gravity assists don't have to be simple, though. Nimur (talk) 20:53, 3 August 2010 (UTC)

In any event, a gravity assist maneuver isn't bound to the plane of the ecliptic -- Voyager 1 was moderately deflected out of the ecliptic by Titan, and Voyager 2 is on a track 55° relative to the ecliptic. Probes such as Ulysses have been sent on solar polar orbits. The only reason we don't go outside the ecliptic very much is that there just isn't much there that's within a useful distance. In terms of interstellar travel, it both matters and it doesn't. On one hand, it matters because it's a significant proportional speed boost. On the other, it's still stupidly slow when you talk about interstellar travel, because arriving in 70,000 years (the length of time it would take Voyager 1 to reach Proxima Centauri, assuming that the Sun's gravity magically vanished) is functionally the same as never arriving at all. — Lomn 20:57, 3 August 2010 (UTC)

The Earth's orbital speed and gravity assists would help with travelling in or near the ecliptic, but I don't think they would be significant. The Earth's orbital speed is 0.01% the speed of light. I don't think it's really practical to do interstellar travel at much less than 10% the speed of light, so the Earth's orbital speed (and that of any planets you might use for gravity assists) is negligible. It makes far more sense to decide on stars to visit based on their distance from us and how interesting they are. --Tango (talk) 23:31, 3 August 2010 (UTC)

That is an interesting question, the answer depends on your definition of “travel” and “current technology”. With current technology we can not travel to other stars as in living humans reaching any other star, with or without gravity-assist. If a non-functional space-probe reaching a other star system in some million years is counted as travel it is easiest about the plane of the ecliptic, we need not do any thing at all since Voyager 1 will do that. Voyager 1 has a speed of 17 km/s and after exiting the suns gravity it will have an speed of 13 km/s. If it was directed at Proxima Centauri it would reach it in about 100 000 years.(Neglecting the relative motion between the sun and Proxima Centauri.)

In order to reach a other star a spacecraft on earth need deltaV to leave the earth's gravity (11 km/s), leave the suns gravity (ca 12 km/s), reach a cruse speed and de-accelerate at the other star if it is not a flyby mission.

The cruse speed needed for different travel time to Proxima Centauri with no compensation for acceleration time, the relative motion between the sun and Proxima Centauri or relativistic effects:

traveltime (years)	speed (km/s)
10 000	120
1000	1200
100	12000
10	120000

The greatest increase in speed by an unpowered gravity-assist for the four gas giants are:

Sun	0 km/s
Jupiter	26 km/s
Saturn	20 km/s
Uranus	14 km/s
Neptune	11 km/s

These can not be combined fully and the inner planets could give some help, I have not worked out the math but I expect the maximum increase in speed to be less than 50 km/s. With somewhat lower increase in speed, gravity-assist can be used to change the direction out of the ecliptic plane.

The greatest additional increase of speed for a powered gravity-assist possible in the solar system is about 300 km/s and is obtained by firing the engines just above the solar surface. The radiation temperature of about 4500 celsius during some hours could be a problem.

A powered gravity-assist around the sun can with minimal extra effort be used for a mission in any direction.

For missions longer than 1000 years gravity-assist could have some utility but even then the direction is of low significance, for faster missions gravity-assist within the solar system gives insignificant extra speed.

--Gr8xoz (talk) 23:57, 3 August 2010 (UTC)

One note: Voyager 1 has a speed of 17 km/s and after exiting the Sun's gravity it will still have a speed of 17 km/s (rounded), see Specific orbital energy#Voyager 1.--Patrick (talk) 05:47, 4 August 2010 (UTC)

My mistake, the escape velocity at the position of Voyager 1 is 4 km/s but the substraction must be done with orbital energy not speed.--Gr8xoz (talk) 07:54, 4 August 2010 (UTC)

I made some more mistakes, a powered gravity-assist just above the solar surface could give an extra speed of 600 km/s not 300 km/s and the extra deltaV for escaping the gravity of the sun and the earth can not be directly added to the deltaV budget. Given this, powered gravity-assist could theoretically have some significance for missions longer than about 200 years, in that case 6000 km/s is needed (+de-acceleration) and 600 km/s can be obtained for "free" by powered gravity-assist.--Gr8xoz (talk) 08:45, 4 August 2010 (UTC)